System and process for gas sweetening

ABSTRACT

A method for removing hydrogen sulfide from a sour gas stream comprising hydrogen sulfide by oxidizing hydrogen sulfide in a converter by contacting the sour gas stream with an aqueous catalytic solution, thereby producing a desulfurized gas stream and a liquid stream comprising reduced catalyst and elemental sulfur, introducing an oxidant and the liquid stream comprising reduced catalyst and elemental sulfur into a high shear device and producing a dispersion wherein the mean bubble diameter of the oxidant gas in the dispersion is less than about 5 μm, introducing the dispersion into a vessel from which a sulfur-containing slurry is removed and a regenerated catalyst stream is removed, wherein the sulfur slurry comprises elemental sulfur and aqueous liquid, and recycling at least a portion of the regenerated catalyst stream to the converter. A system of apparatus for carrying out the method is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims the benefitunder 35 U.S.C. §121 of U.S. patent application Ser. No. 12/138,260,filed Jun. 12, 2008, which claims the benefit under 35 U.S.C. §119(e) ofU.S. Provisional Patent Application No. 60/946,459, filed Jun. 27, 2007,the disclosures of each of which are hereby incorporated herein byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to the desulfurization of gasstreams containing hydrogen sulfide. More particularly, the presentinvention relates to a high shear system and method for catalyticallyoxidizing hydrogen sulfide in liquid streams comprising hydrogen sulfideto elemental sulfur and regenerating reduced catalyst for recycle byoxidation.

2. Background of the Invention

Many processes produce fluid streams comprising hydrogen sulfide. Often,hydrogen sulfide must be removed from a gas prior to venting the gas fordisposal or further treatment. For example, hydrogen sulfide is anuisance odor from wastewater treatment plants and facilities comprisingreverse osmosis systems. Hydrogen sulfide can also be anaturally-present component in energy sources, including natural gas,oil, biogas, synthesis gas, geothermal gas streams, and others.Hydrodesulfurization of liquid streams by hydrogen treatment in thepresence of a hydrodesulfurization catalyst is frequently used toconvert organic sulfur compounds to hydrogen sulfide. The hydrogensulfide must then be removed from the liquid streams. Combustion ofhydrogen sulfide produces sulfur dioxide, which is believed to lead tothe production of acid rain and potential destruction of theenvironment. Furthermore, when contacted with water, hydrogen sulfideforms sulfuric acid which is corrosive to the metals of processapparatus.

One commercial desulfurization process is the LO-CAT process of GasTechnology Products, LLC of Schaumberg, Ill. The Lo-CAT process is amethod for performing a modified Claus reaction. The Lo Cat process is awet scrubbing, liquid redox system that uses a chelated iron solution(homogeneous catalytic, i.e. ‘LoCat’, solution) to convert H₂S toelemental sulfur.

A considerable amount of effort has been devoted to developing masstransfer devices which improve the oxygen utilization in conventionalliquid oxidation systems (such as the Lo-CAT system) with the aim ofreducing the quantity of air required (operating cost) and reducing thesize of the oxidizing vessels (capital cost). Currently, there are twotypes of oxidizers employed: low head and high head oxidizers. In lowhead oxidizers, air is sparged through approximately 3 meters ofsolution at superficial air velocities of less than 3.5 m/min by meansof distributors equipped with EPDM (ethylene propylene diene monomer)sleeves which are perforated with very small holes. Solution flow isperpendicular to the airflow. Such low head oxidizers are relativelypoor mass transfer devices. Low head oxidizers do, however, provide muchneeded solution inventory for proper operation of the system.

In high head oxidizers, air is sparged through approximately 7 meters ofsolution at superficial velocities of greater than 10 m/min by means ofcoarse bubble pipe distributors. Solution flow is co-current to theairflow in high head oxidizers. These oxidizers provide mass transfercoefficients which are approximately 4 times better than those of lowhead oxidizers; however, this is at the expense of higher dischargeheads on the air blowers.

Accordingly, there is a need in industry for improved processes fordesulfurizing (i.e. sweetening) gas streams.

SUMMARY

High shear systems and methods for improving removing hydrogen sulfidefrom gas streams are disclosed. In accordance with certain embodiments,a method for gas sweetening is provided for removing hydrogen sulfidefrom a sour gas stream comprising hydrogen sulfide, the methodcomprising: oxidizing hydrogen sulfide in a converter by contacting thesour gas stream with an aqueous catalytic solution, thereby producing adesulfurized gas stream and a liquid stream comprising reduced catalystand elemental sulfur; introducing an oxidant and the liquid streamcomprising reduced catalyst and elemental sulfur into a high sheardevice and producing a dispersion wherein the mean bubble diameter ofthe oxidant gas in the dispersion is less than about 5 μm; introducingthe dispersion into a vessel from which a sulfur-containing slurry isremoved and a regenerated catalyst stream is removed, wherein the sulfurslurry comprises elemental sulfur and aqueous liquid; and recycling atleast a portion of the regenerated catalyst stream to the converter. Themethod may further comprise removing at least a portion of the aqueoussolution from the sulfur-containing slurry and recycling at least afraction of the recovered aqueous solution to the vessel. Inembodiments, the vessel is an oxidizer comprising spargers wherebyadditional oxidant gas is introduced into the vessel.

Also disclosed herein is a method for sweetening a sour gas stream, themethod comprising: forming a dispersion comprising oxidant gas bubblesdispersed in a liquid phase comprising reduced redox liquid catalyst,wherein the bubbles have a mean diameter of less than 1 micron. The gasbubbles may have a mean diameter of less than 400 nm. In embodiments,the gas bubbles have a mean diameter of no more than 100 nm. The sourgas may comprise a gas selected from the group consisting of air,natural gas, carbon dioxide, amine acid gas, landfill gas, biogas,synthesis gas, geothermal gas, refinery gas, and combinations thereof.In embodiments, forming the dispersion comprises subjecting a mixture ofthe oxidant gas and the liquid catalytic phase to a shear rate ofgreater than about 20,000 s⁻¹. Forming the dispersion may comprisecontacting the oxidant gas and the liquid catalytic phase in a highshear device, wherein the high shear device comprises at least onerotor, and wherein the at least one rotor is rotated at a tip speed ofat least 22.9 m/s (4,500 ft/min) during formation of the dispersion. Thehigh shear device may produce a local pressure of at least about 1034.2MPa (150,000 psi) at the tip of the at least one rotor. The energyexpenditure of the high shear device may be greater than 1000 W/m³. Inembodiments, the redox catalyst is selected from organometallics andiron chelate catalysts.

Also disclosed is a method for removing hydrogen sulfide from sour gas,the method comprising: oxidizing hydrogen sulfide gas by contacting thesour gas with a liquid comprising an oxidized catalyst in a converter toproduce a converter liquid product stream comprising sulfur and reducedcatalyst; forming a fluid mixture comprising the converter liquidproduct stream and oxidant gas; exposing the fluid mixture to a shearrate of at least about 20,000 s⁻¹ to produce a dispersion of oxidant ina continuous phase of the liquid; and introducing the dispersion into avessel from which a sulfur slurry is removed and from which a liquidstream comprising regenerated oxidized liquid catalyst is recycled tothe converter. The method may further comprise: introducing the sulfurslurry to a separator from which aqueous liquid in the slurry is removedfrom the sulfur; and recycling the aqueous liquid removed from theslurry to the vessel. The average bubble diameter of the oxidant gas inthe dispersion may be less than 1 μm. The dispersion may be stable forat least about 15 minutes at atmospheric pressure. In embodiments,exposing the fluid mixture to a shear rate of greater than about 20,000s⁻¹ comprises introducing the fluid into a high shear device comprisingat least two generators.

Also disclosed is a system for removing hydrogen sulfide from a sour gasstream, the system comprising: a converter comprising an inlet for sourgas, an inlet for a liquid stream comprising oxidized catalyst, and anoutlet line for a converter liquid product comprising sulfur and reducedliquid catalyst; a dispersible gas inlet whereby oxidant may beintroduced into the outlet line; an external high shear devicedownstream of the dispersible gas inlet, the external high shear devicecomprising an inlet in fluid communication with the converter outletline, and a high shear device outlet; an oxidizer in fluid communicationwith the high shear device outlet; and a recycle line fluidly connectingthe oxidizer and the inlet line for a liquid stream of the converter,whereby regenerated oxidized catalyst may be recycled to the converter.The external high shear device may comprise a toothed rim dispersercomprising at least one generator set comprising a rotor and a statorhaving a shear gap width defined as the minimum clearance between therotor and the stator, wherein the rotor is rotatable at a tip speedwhereby the shear rate defined as the tip speed divided by the shear gapwidth is at least 100,000 s⁻¹ is produced. The external high sheardevice may have a tip speed of greater than 20.3 m/s (4000 ft/min). Inembodiments, the external high shear device is capable of producing adispersion of oxidant bubbles in aqueous catalytic solution, the oxidantbubbles having an average bubble diameter on the submicrometer scale.The system may comprise at least two high shear devices.

Also disclosed is an improvement in a system for removing hydrogensulfide from a sour gas stream, the system comprising an absorptionunit, a redox catalyst that becomes reduced upon converting hydrogensulfide to elemental sulfur, an oxidization unit for regenerating thereduced catalyst, and a catalyst recycling system for returningregenerated catalyst to the absorption unit, the improvement comprising:inserting a high shear device in line between the converter and theoxidization unit, the high shear device comprising at least twogenerators, wherein at least one of the generators produces a shear rateof at least 10,000 s⁻¹. The shear rate provided by one generator may begreater than the shear rate provided by another generator.

Some embodiments of the system potentially make possible the sweeteningof gas streams without the need for large volume reactors, via use of anexternal pressurized high shear reactor.

Certain embodiments of an above-described method or system potentiallyprovide for more optimal time, temperature and pressure conditions thanare otherwise possible, and which potentially increase the rate of themultiphase process. Certain embodiments of the above-described methodsor systems potentially provide overall cost reduction by operating atlower temperature and/or pressure, providing increased product per unitof catalyst consumed, decreased reaction time, and/or reduced capitaland/or operating costs. These and other embodiments and potentialadvantages will be apparent in the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiment of thepresent invention, reference will now be made to the accompanyingdrawings, wherein:

FIG. 1 is a schematic of a high shear gas sweetening system comprisingexternal high shear dispersing according to an embodiment of the presentdisclosure.

FIG. 2 is a longitudinal cross-section view of a multi-stage high sheardevice, as employed in an embodiment of the system.

FIG. 3 is a box flow diagram of a high shear desulfurization processaccording to an embodiment of the present disclosure.

NOTATION AND NOMENCLATURE

As used herein, the term “dispersion” refers to a liquefied mixture thatcontains at least two distinguishable substances (or “phases”) that willnot readily mix and dissolve together. As used herein, a “dispersion”comprises a “continuous” phase (or “matrix”), which holds thereindiscontinuous droplets, bubbles, and/or particles of the other phase orsubstance. The term dispersion may thus refer to foams comprising gasbubbles suspended in a liquid continuous phase, emulsions in whichdroplets of a first liquid are dispersed throughout a continuous phasecomprising a second liquid with which the first liquid is immiscible,and continuous liquid phases throughout which solid particles aredistributed. As used herein, the term “dispersion” encompassescontinuous liquid phases throughout which gas bubbles are distributed,continuous liquid phases throughout which solid particles (e.g., solidcatalyst) are distributed, continuous phases of a first liquidthroughout which droplets of a second liquid that is substantiallyinsoluble in the continuous phase are distributed, and liquid phasesthroughout which any one or a combination of solid particles, immiscibleliquid droplets, and gas bubbles are distributed. Hence, a dispersioncan exist as a homogeneous mixture in some cases (e.g., liquid/liquidphase), or as a heterogeneous mixture (e.g., gas/liquid, solid/liquid,or gas/solid/liquid), depending on the nature of the materials selectedfor combination.

DETAILED DESCRIPTION Overview

The rate of chemical reactions involving liquids, gases and solidsdepend on time of contact, temperature, and pressure. In cases where itis desirable to react two or more raw materials of different phases(e.g. solid and liquid; liquid and gas; solid, liquid and gas), one ofthe limiting factors controlling the rate of reaction involves thecontact time of the reactants. In the case of heterogeneously catalyzedreactions there is the additional rate limiting factor of having thereacted products removed from the surface of the catalyst to permit thecatalyst to catalyze further reactants. Contact time for the reactantsand/or catalyst is often controlled by mixing which provides contactwith two or more reactants involved in a chemical reaction.

A reactor assembly that comprises an external high shear device or mixeras described herein makes possible decreased mass transfer limitationsand thereby allows the reaction to more closely approach kineticlimitations. When reaction rates are accelerated, residence times may bedecreased, thereby increasing obtainable throughput. Product yield maybe increased as a result of the high shear system and process.Alternatively, if the product yield of an existing process isacceptable, decreasing the required residence time by incorporation ofsuitable high shear may allow for the use of lower temperatures and/orpressures than conventional processes.

Furthermore, without wishing to be limited by theory, it is believedthat the high shear conditions provided by a reactor assembly thatcomprises an external high shear device or mixer as described herein maypermit gas sweetening at global operating conditions under whichreaction may not conventionally be expected to occur to any significantextent.

System for Gas Sweetening. A high shear gas sweetening system will nowbe described in relation to FIG. 1, which is a process flow diagram ofan embodiment of a high shear system 1 for removing hydrogen sulfidefrom a gas stream comprising hydrogen sulfide. High shear sulfur removalsystem 1 can be thought of as having four process zones; converter(absorber), high shear device/oxidizer, oxidizer/sulfur separation, andsulfur handling. The basic components of a representative high shearsystem for liquid reduction oxidation desulfurization include converter30, external high shear device (HSD) 40, vessel 10, and pump 5. As shownin FIG. 1, high shear device 40 is located external to vessel/reactor10. Each of these components is further described in more detail below.Line 25 introduces gas containing hydrogen sulfide into converter 30. Insome applications, high shear gas sweetening system 1 further comprisessour gas feed stream pretreatment, such as, for example, knock out pot24. Knock-out pot 24 may be fed via inlet line 23 through which sour gasis fed into high shear gas sweetening system 1. Line 25 may connectknock-out pot 24 with converter 30.

Line 21 may be connected to pump 5 for introducing liquid catalyst intoconverter 30. Pump 5 may be, in some embodiments, positioned elsewherethroughout high shear gas sweetening system 1, for example, betweenconverter 30 and HSD 40. Treated gas exits converter 30 via line 35.Line 13 connects converter 30 to HSD 40, and line 18 fluidly connectsHSD 40 with vessel 10. Line 22 may be connected to line 13 forintroducing oxidant (e.g., air or enriched air) into HSD 40.Alternatively, line 22 may be connected directly to an inlet of HSD 40.High shear gas sweetening system 1 may further comprise venture sparger45, which may be connected to HSD 40 via line 18 and to vessel 10 vialine 19. Line 17 may be connected to vessel 10 for removal of vent gas.Additional components or process steps may be incorporated throughouthigh shear gas sweetening system 1, for example, between vessel 10 andHSD 40, or ahead of pump 5 or HSD 40, if desired, for example, heatexchangers. Line 21 connects vessel 10 with converter 30 to provide forcatalyst recycle, if desired.

In some applications, high shear gas sweetening system 1 furthercomprises sulfur separation apparatus, for example, sulfur settler 60,slurry pump 70, settler feed pump 50, or a combination thereof. Settlerfeed pump 50 may be fluidly connected via line 16 to oxidizer vessel 10whereby a sulfur slurry is extracted from vessel 10. Line 51 may connectan outlet of settler feed pump 50 with sulfur settler 60 via line 53 andto oxidizer vessel 10 via line 52.

Sulfur settler 60 may be connected to slurry pump 70 via line 65. Line75 may be connected to slurry pump 70 and may be used to send sulfur forfurther separation 80. Aqueous catalytic solution separated in settler60 may be returned to vessel 10 via line 14.

High shear gas sweetening system 1 may further comprise air blower 90.Air blower 90 may be connected to vessel 10 to provide optionalsecondary air to vessel 10. Air blower 90 may be connected to filter andsilencer 85.

Converter. Converter 30 comprises a contactor in which sour gas iscontacted with a homogeneous liquid catalyst solution. Converter 30 maybe referred to as an absorber. In embodiments, any liquid reductionoxidation catalyst suitable for oxidizing hydrogen sulfide to produceelemental sulfur is employed. These include, for example, catalystscomprising chelate of iron or other organometallics. In embodiments, thedesulfurization reaction is carried out in the aqueous phase usingchelated iron as the catalytic reagent. Chelating agents are organiccompounds which wrap around iron ions in a claw-like fashion to formchemical bonds between two or more non-iron atoms and the iron atom. Thesystem is typically operated in the mildly alkaline pH range to insuregood absorption of H₂S into the slightly alkaline liquid catalystsolution. A suitable catalyst is the LoCat solution of Gas TechnologyProducts LLC. Liquid homogeneous catalytic solution 21 may be introducedinto converter 30 via pump 5 and converter inlet line 12. Inembodiments, liquid catalytic solution flows countercurrently to sourgas flow through converter 30. In embodiments, converter 30 is a spargedabsorber. In such an embodiment, acid gas from line 25 is sparged intoconverter 30. Hydrogen sulfide in the sour gas is oxidized by reactionwith the catalyst to form elemental sulfur, and the catalyst is reduced.The catalyst circulates through converter 30 by the lift generated by,for example, sparging. Treated gas from which hydrogen sulfide has beenremoved exits converter 30 via line 35. Converter liquid productcomprising elemental sulfur and reduced catalyst exits converter 30 vialine 13.

High Shear Device. External high shear device (HSD) 40, also sometimesreferred to as a high shear device or a high shear mixing device, isconfigured for receiving an inlet stream via line 13, comprisingconverter liquid product and oxidant. Oxidant is introduced into highshear device 40 via dispersible gas line 22, which may inject oxidantinto line 13 upstream of HSD 40. Alternatively, HSD 40 may be configuredfor receiving the liquid and oxidant reactant streams via separate inletlines (not shown). Although only one high shear device is shown in FIG.1, it should be understood that some embodiments of the system may havetwo or more high shear mixing devices arranged either in series orparallel flow. HSD 40 is a mechanical device that utilizes one or moregenerator comprising a rotor/stator combination, each of which has a gapbetween the stator and rotor. The gap between the rotor and the statorin each generator set may be fixed or may be adjustable. HSD 40 isconfigured in such a way that it is capable of producing submicron andmicron-sized bubbles in a reactant mixture flowing through the device.The high shear device comprises an enclosure or housing so that thepressure and temperature of the reaction mixture may be controlled.

High shear mixing devices are generally divided into three generalclasses, based upon their ability to mix fluids. Mixing is the processof reducing the size of particles or inhomogeneous species within thefluid. One metric for the degree or thoroughness of mixing is the energydensity per unit volume that the mixing device generates to disrupt thefluid particles. The classes are distinguished based on delivered energydensities. Three classes of industrial mixers having sufficient energydensity to consistently produce mixtures or emulsions with particlesizes in the range of submicron to 50 microns include homogenizationvalve systems, colloid mills and high speed mixers. In the first classof high energy devices, referred to as homogenization valve systems,fluid to be processed is pumped under very high pressure through anarrow-gap valve into a lower pressure environment. The pressuregradients across the valve and the resulting turbulence and cavitationact to break-up any particles in the fluid. These valve systems are mostcommonly used in milk homogenization and can yield average particlesizes in the submicron to 1 micron range.

At the opposite end of the energy density spectrum is the third class ofdevices referred to as low energy devices. These systems usually havepaddles or fluid rotors that turn at high speed in a reservoir of fluidto be processed, which in many of the more common applications is a foodproduct. These low energy systems are customarily used when averageparticle sizes of greater than 20 microns are acceptable in theprocessed fluid.

Between the low energy devices and homogenization valve systems, interms of the mixing energy density delivered to the fluid, are colloidmills and high shear rotor-stator dispersers, which are classified asintermediate energy devices. A typical colloid mill configurationincludes a conical or disk rotor that is separated from a complementary,liquid-cooled stator by a closely-controlled rotor-stator gap, which iscommonly between 0.0254 mm to 10.16 mm (0.001-0.40 inch). Rotors areusually driven by an electric motor through a direct drive or beltmechanism. As the rotor rotates at high rates, it pumps fluid betweenthe outer surface of the rotor and the inner surface of the stator, andshear forces generated in the gap process the fluid. Many colloid millswith proper adjustment achieve average particle sizes of 0.1-25 micronsin the processed fluid. These capabilities render colloid millsappropriate for a variety of applications including colloid andoil/water-based emulsion processing such as that required for cosmetics,mayonnaise, or silicone/silver amalgam formation, to roofing-tar mixing.

Tip speed is the circumferential distance traveled by the tip of therotor per unit of time. Tip speed is thus a function of the rotordiameter and the rotational frequency. Tip speed (in meters per minute,for example) may be calculated by multiplying the circumferentialdistance transcribed by the rotor tip, 2πR, where R is the radius of therotor (meters, for example) times the frequency of revolution (forexample revolutions per minute, rpm). A colloid mill, for example, mayhave a tip speed in excess of 22.9 m/s (4500 ft/min) and may exceed 40m/s (7900 ft/min). For the purpose of this disclosure, the term ‘highshear’ refers to mechanical rotor stator devices (e.g., colloid mills orrotor-stator dispersers) that are capable of tip speeds in excess of 5.1m/s (1000 ft/min) and require an external mechanically driven powerdevice to drive energy into the stream of products to be reacted. Forexample, in HSD 40, a tip speed in excess of 22.9 m/s (4500 ft/min) isachievable, and may exceed 40 m/s (7900 ft/min). In some embodiments,HSD 40 is capable of delivering at least 300 L/h at a tip speed of atleast 22.9 m/s (4500 ft/min). The power consumption may be about 1.5 kW.HSD 40 combines high tip speed with a very small shear gap to producesignificant shear on the material being processed. The amount of shearwill be dependent on the viscosity of the fluid. Accordingly, a localregion of elevated pressure and temperature is created at the tip of therotor during operation of the high shear device. In some cases thelocally elevated pressure is about 1034.2 MPa (150,000 psi). In somecases the locally elevated temperature is about 500° C. In some cases,these local pressure and temperature elevations may persist for nano orpico seconds.

An approximation of energy input into the fluid (kW/L/min) can beestimated by measuring the motor energy (kW) and fluid output (L/min).As mentioned above, tip speed is the velocity (ft/min or m/s) associatedwith the end of the one or more revolving elements that is creating themechanical force applied to the reactants. In embodiments, the energyexpenditure of HSD 40 is greater than 1000 W/m³. In embodiments, theenergy expenditure of HSD 40 is in the range of from about 3000 W/m³ toabout 7500 W/m³.

The shear rate is the tip speed divided by the shear gap width (minimalclearance between the rotor and stator). The shear rate generated in HSD40 may be in the greater than 20,000 s⁻¹. In some embodiments the shearrate is at least 40,000 s⁻¹. In some embodiments the shear rate is atleast 100,000 s⁻¹. In some embodiments the shear rate is at least500,000 s⁻¹. In some embodiments the shear rate is at least 1,000,000s⁻¹. In some embodiments the shear rate is at least 1,600,000 s⁻¹. Inembodiments, the shear rate generated by HSD 40 is in the range of from20,000 s⁻¹ to 100,000 s⁻¹. For example, in one application the rotor tipspeed is about 40 m/s (7900 ft/min) and the shear gap width is 0.0254 mm(0.001 inch), producing a shear rate of 1,600,000 s⁻¹. In anotherapplication the rotor tip speed is about 22.9 m/s (4500 ft/min) and theshear gap width is 0.0254 mm (0.001 inch), producing a shear rate ofabout 901,600 s⁻¹.

HSD 40 is capable of highly dispersing or transporting oxidant gas intoa main liquid phase (continuous phase) comprising reduced liquidcatalyst, with which it would normally be immiscible, at conditions suchthat at least a portion of the liquid catalyst is oxidized. In someembodiments, HSD 40 comprises a colloid mill. Suitable colloidal millsare manufactured by IKA® Works, Inc. Wilmington, N.C. and APV NorthAmerica, Inc. Wilmington, Mass., for example. In some instances, HSD 40comprises the DISPAX REACTOR® of IKA® Works, Inc.

The high shear device comprises at least one revolving element thatcreates the mechanical force applied to the reactants. The high sheardevice comprises at least one stator and at least one rotor separated bya clearance. For example, the rotors may be conical or disk shaped andmay be separated from a complementarily-shaped stator. In embodiments,both the rotor and stator comprise a plurality ofcircumferentially-spaced teeth. In some embodiments, the stator(s) areadjustable to obtain the desired shear gap between the rotor and thestator of each generator (rotor/stator set). Grooves between the teethof the rotor and/or stator may alternate direction in alternate stagesfor increased turbulence. Each generator may be driven by any suitabledrive system configured for providing the necessary rotation.

In some embodiments, the minimum clearance (shear gap width) between thestator and the rotor is in the range of from about 0.0254 mm (0.001inch) to about 3.175 mm (0.125 inch). In certain embodiments, theminimum clearance (shear gap width) between the stator and rotor isabout 1.52 mm (0.060 inch). In certain configurations, the minimumclearance (shear gap) between the rotor and stator is at least 1.78 mm(0.07 inch). The shear rate produced by the high shear device may varywith longitudinal position along the flow pathway. In some embodiments,the rotor is set to rotate at a speed commensurate with the diameter ofthe rotor and the desired tip speed. In some embodiments, the high sheardevice has a fixed clearance (shear gap width) between the stator androtor. Alternatively, the high shear device has adjustable clearance(shear gap width).

In some embodiments, HSD 40 comprises a single stage dispersing chamber(i.e., a single rotor/stator combination, a single generator). In someembodiments, high shear device 40 is a multiple stage inline disperserand comprises a plurality of generators. In certain embodiments, HSD 40comprises at least two generators. In other embodiments, high sheardevice 40 comprises at least 3 high shear generators. In someembodiments, high shear device 40 is a multistage mixer whereby theshear rate (which, as mentioned above, varies proportionately with tipspeed and inversely with rotor/stator gap width) varies withlongitudinal position along the flow pathway, as further describedherein below.

In some embodiments, each stage of the external high shear device hasinterchangeable mixing tools, offering flexibility. For example, the DR2000/4 DISPAX REACTOR® of IKA® Works, Inc. Wilmington, N.C. and APVNorth America, Inc. Wilmington, Mass., comprises a three stagedispersing module. This module may comprise up to three rotor/statorcombinations (generators), with choice of fine, medium, coarse, andsuper-fine for each stage. This allows for creation of dispersionshaving a narrow distribution of the desired bubble size (e.g., oxidantgas bubbles). In some embodiments, each of the stages is operated withsuper-fine generator. In some embodiments, at least one of the generatorsets has a minimum rotor/stator clearance (shear gap width) of greaterthan about 5.08 mm (0.20 inch). In alternative embodiments, at least oneof the generator sets has a minimum rotor/stator clearance of greaterthan about 1.78 mm (0.07 inch).

Referring now to FIG. 2, there is presented a longitudinal cross-sectionof a suitable high shear device 200. High shear device 200 of FIG. 2 isa dispersing device comprising three stages or rotor-statorcombinations. High shear device 200 is a dispersing device comprisingthree stages or rotor-stator combinations, 220, 230, and 240. Therotor-stator combinations may be known as generators 220, 230, 240 orstages without limitation. Three rotor/stator sets or generators 220,230, and 240 are aligned in series along drive shaft 250.

First generator 220 comprises rotor 222 and stator 227. Second generator230 comprises rotor 223 and stator 228. Third generator 240 comprisesrotor 224 and stator 229. For each generator the rotor is rotatablydriven by input 250 and rotates about axis 260 as indicated by arrow265. The direction of rotation may be opposite that shown by arrow 265(e.g., clockwise or counterclockwise about axis of rotation 260).Stators 227, 228, and 229 are fixably coupled to the wall 255 of highshear device 200.

As mentioned hereinabove, each generator has a shear gap width which isthe minimum distance between the rotor and the stator. In the embodimentof FIG. 2, first generator 220 comprises a first shear gap 225; secondgenerator 230 comprises a second shear gap 235; and third generator 240comprises a third shear gap 245. In embodiments, shear gaps 225, 235,245 have widths in the range of from about 0.025 mm to about 10.0 mm.Alternatively, the process comprises utilization of a high shear device200 wherein the gaps 225, 235, 245 have a width in the range of fromabout 0.5 mm to about 2.5 mm. In certain instances the shear gap widthis maintained at about 1.5 mm. Alternatively, the width of shear gaps225, 235, 245 are different for generators 220, 230, 240. In certaininstances, the width of shear gap 225 of first generator 220 is greaterthan the width of shear gap 235 of second generator 230, which is inturn greater than the width of shear gap 245 of third generator 240. Asmentioned above, the generators of each stage may be interchangeable,offering flexibility. High shear device 200 may be configured so thatthe shear rate will increase stepwise longitudinally along the directionof the flow 260.

Generators 220, 230, and 240 may comprise a coarse, medium, fine, andsuper-fine characterization. Rotors 222, 223, and 224 and stators 227,228, and 229 may be toothed designs. Each generator may comprise two ormore sets of rotor-stator teeth. In some embodiments, rotors 222, 223,and 224 comprise more than ten rotor teeth circumferentially spacedabout the circumference of each rotor. in embodiments, stators 227, 228,and 229 comprise more than 10 stator teeth circumferentially spacedabout the circumference of each stator. In embodiments, the innerdiameter of the rotor is about 12 cm. In embodiments, the diameter ofthe rotor is about 6 cm. In embodiments, the outer diameter of thestator is about 15 cm. In embodiments, the diameter of the stator isabout 6.4 cm. In some embodiments the rotors are 60 mm and the statorsare 64 mm in diameter, providing a clearance of about 4 mm. In certainembodiments, each of three stages is operated with a super-finegenerator, comprising a shear gap of between about 0.025 mm and about 4mm.

High shear device 200 is configured for receiving from line 13 areactant stream at inlet 205. The reaction mixture comprises oxidant gasas the dispersible phase and liquid comprising reduced catalyst as thecontinuous phase. Feed stream entering inlet 205 is pumped seriallythrough generators 220, 230, and then 240, such that product dispersionis formed. Product dispersion exits high shear device 200 via outlet 210(and line 18 of FIG. 1). The rotors 222, 223, 224 of each generatorrotate at high speed relative to the fixed stators 227, 228, 229,producing a high shear rate. The rotation of the rotors pumps fluid,such as the feed stream entering inlet 205, outwardly through the sheargaps (and, if present, through the spaces between the rotor teeth andthe spaces between the stator teeth), creating a localized high shearcondition. High shear forces exerted on fluid in shear gaps 225, 235,and 245 (and, when present, in the gaps between the rotor teeth and thestator teeth) through which fluid flows process the fluid and createproduct dispersion. Product dispersion exits high shear device 200 viahigh shear outlet 210 (and line 18 of FIG. 1).

The product dispersion has an average gas bubble size less than about 5μm. In embodiments, HSD 40 produces a dispersion having a mean bubblesize of less than about 1.5 μm. In embodiments, HSD 40 produces adispersion having a mean bubble size of less than 1 μm; preferably thebubbles are sub-micron in diameter. In certain instances, the averagebubble size is from about 0.1 μm to about 1.0 μm. In embodiments, HSD 40produces a dispersion having a mean bubble size of less than 400 nm. Inembodiments, HSD 40 produces a dispersion having a mean bubble size ofless than 100 nm. High shear device 200 produces a dispersion comprisingdispersed gas bubbles capable of remaining dispersed at atmosphericpressure for at least about 15 minutes.

The bubbles of oxidant gas in the product dispersion created by highshear device 200 facilitate and/or accelerate the oxidation of thecatalyst by enhancing contact of the reactants. The rotor may be set torotate at a speed commensurate with the diameter of the rotor and thedesired tip speed as described hereinabove.

In certain instances, high shear device 200 comprises a DISPAX REACTOR®of IKA® Works, Inc. Wilmington, N.C. and APV North America, Inc.Wilmington, Mass. Several models are available having variousinlet/outlet connections, horsepower, tip speeds, output rpm, and flowrate. Selection of the high shear device will depend on throughputrequirements and desired particle or bubble size in dispersion in line18 (FIG. 1) exiting outlet 210 of high shear device 200. IKA® model DR2000/4, for example, comprises a belt drive, 4M generator, PTFE sealingring, inlet flange 25.4 mm (1 inch) sanitary clamp, outlet flange 19 mm(¾ inch) sanitary clamp, 2HP power, output speed of 7900 rpm, flowcapacity (water) approximately 300-700 L/h (depending on generator), atip speed of from 9.4-41 m/s (1850 ft/min to 8070 ft/min).

Vessel. Vessel or oxidizer 10 is any type of vessel from which a slurryof sulfur product can be separated and within which oxidation ofhomogeneous catalyst may propagate. For instance, a continuous orsemi-continuous stirred tank reactor, or one or more batch reactors maybe employed in series or in parallel. In some applications vessel 10 isan oxidizer. Oxidant may be introduced into vessel 10 from an optionalsecondary air source via blower 90 and line 15. Oxidant may beintroduced through spargers which may line the cross-section of vessel10 above the bottom section of the vessel in which sulfur slurrysettles. Sulfur slurry may be removed from a cone-shaped bottom of thevessel 10. Any number of inlet lines to vessel 10 is envisioned, withthree shown in FIG. 1 (lines 14, 15 and 52). Inlet line 14 may be aninlet line connected to sulfur settler 60 and designed for the return tovessel 10 of liquid catalytic solution separated from product sulfurslurry. Inlet line 15 may be utilized to provide optional secondary airvia blower 90. Line 52 may connect the outlet of pump 50 in line 51 tovessel 10. Vessel 10 may comprise an exit line 17 for vent gas, and anoutlet product line 16 for a product stream comprising a slurry ofsulfur in liquid solution. In embodiments, vessel 10 comprises aplurality of reactor product lines 16. Line 21 may connectvessel/oxidizer 10 with converter 30 via pump 5 and line 12.

Oxidation of homogeneous catalyst will occur whenever suitable time,temperature and pressure conditions exist. In this sense catalystoxidation may occur at any point in the flow diagram of FIG. 1 iftemperature and pressure conditions are suitable. Due to the use of aliquid catalyst, substantial oxidation of the reduced catalyst may occurat points outside oxidizer/vessel 10 shown in FIG. 1. Nonetheless adiscrete reactor/vessel 10 is often desirable to allow for increasedresidence time, agitation and heating and/or cooling. In embodiments, itis envisioned that substantial oxidation/regeneration of the catalystwill occur within HSD 40 (or a series or parallel combination of highshear devices 40). In such instances, vessel 10 may serve primarily as aseparator from which a slurry of sulfur may be removed for sulfurprocessing via line 16 and from which regenerated (oxidized) liquidcatalyst is returned to converter 30 for reuse, via line 21. In suchembodiments, optional secondary air source line 15, air blower 90, andfilter/silencer 85 may be absent from the system, or may serve toprovide air only to one or more HSD 40 via line 22.

Vessel 10 may include one or more of the following components: heatingand/or cooling capabilities, pressure measurement instrumentation,temperature measurement instrumentation, one or more injection points,and level regulator (not shown), as are known in the art of reactionvessel design. A heating and/or cooling apparatus may comprise, forexample, a heat exchanger. Alternatively, as much of the conversionreaction may occur within HSD 40 in some embodiments, vessel 10 mayserve primarily as a storage or separation vessel in some cases.Although generally less desired, in some applications vessel 10 may beomitted, particularly if multiple high shear devices/reactors areemployed in series, as further described below.

In alternative embodiments, converter liquid product stream isintroduced into a separator upstream of HSD 40. In this arrangement,sulfur may be removed from converter product in line 13, yielding aliquid catalytic stream comprising reduced liquid catalyst. The reducedliquid catalyst may be introduced into HSD 40 along with oxidant inorder to regenerate the liquid catalyst for reuse in converter 30. Insuch an embodiment, vessel 10 may not be present in high shear gassweetening system 1, as the majority of the regeneration of catalyst mayoccur within HSD 40, or a series of high shear devices 40, and sulfurseparation was performed upstream of the high shear device(s).

Heat Transfer Devices. In addition to the above-mentionedheating/cooling capabilities of vessel 10, other external or internalheat transfer devices for heating or cooling a process stream are alsocontemplated in variations of the embodiments illustrated in FIG. 1. Forexample, if desired, heat may be added to or extracted from vessel 10via any method known to one skilled in the art. The use of externalheating and/or cooling heat transfer devices is also contemplated. Somesuitable locations for one or more such heat transfer devices arebetween pump 5 and converter 30, between HSD 40 and vessel 10, andbetween vessel 10 and pump 5. Some non-limiting examples of such heattransfer devices are shell, tube, plate, and coil heat exchangers, asare known in the art.

Pumps. Pump 5 is configured for either continuous or semi-continuousoperation, and may be any suitable pumping device that is capable ofproviding greater than 202.65 kPa (2 atm) pressure, preferably greaterthan (303.975 kPa (3 atm) pressure, to allow controlled flow through HSD40 and system 1. For example, a Roper Type 1 gear pump, Roper PumpCompany (Commerce Georgia) Dayton Pressure Booster Pump Model 2P372E,Dayton Electric Co (Niles, Ill.) is one suitable pump. Preferably, allcontact parts of the pump comprise stainless steel, for example, 316stainless steel. In some embodiments of the system, pump 5 is capable ofpressures greater than about 2026.5 kPa (20 atm). In addition to pump 5,one or more additional, high pressure pump (not shown) may be includedin the system illustrated in FIG. 1. For example, a booster pump, whichmay be similar to pump 5, may be included between HSD 40 and vessel 10for boosting the pressure into vessel 10. As another example, asupplemental feed pump, which may be similar to pump 5, may be includedfor introducing additional reactants or catalyst into vessel 10. Asstill another example, a compressor type pump may be positioned betweenline 17 and HSD 40 for recycling gas from vessel 10 to HSD 40. Settlerpump 50 may be any pump suitable for extracting a sulfur slurry fromvessel 10.

High Shear Desulfurization Process. FIG. 3 is a box flow diagram showingthe steps in the high shear gas sweetening method. At block 400, H₂S isconverted to elemental sulfur with concomitant reduction of liquid phasecatalyst. At block 500, high shear mixing of iron catalyst with oxidant(e.g., O₂, air, enriched air) produces a dispersion of oxidant in liquidcomprising liquid reduction oxidation catalyst. At block 600, enhancedoxidation of iron catalyst occurs in vessel 10, within HSD 40, or inline 18, optional venture sparger 45, and/or line 19. At block 700return of regenerated (oxidized) catalytic solution to H₂S converter 30proceeds via line 21, pump 5, and line 12. At block 800, recovery ofelemental sulfur and recycle of recovered catalytic solution to oxidizer10 from sulfur recovery units (e.g., from sulfur settler 60) areindicated.

Operation of high shear gas sweetening system 1 will now be discussedwith reference to FIG. 1. In embodiments, the desulfurization reactionis carried out in the aqueous phase using chelated iron as the catalyticreagent. In operation for the desulfurization of sour gas streams, asour gas stream is introduced into system 1 via line 25. Knock-out pot24 may be utilized to remove particulate matter from a sour gasfeedstream introduced into knock-out pot 24 via line 23. Withinconverter 30, sour gas is contacted with oxidized liquid catalyticsolution, which may be introduced countercurrently into converter 30,for example, via line 12.

The system is typically operated in the mildly alkaline pH range toinsure good absorption of the H₂S into the catalyst solution, andalkaline injection and monitoring may occur anywhere suitable withinhigh shear gas sweetening system 1. For example, alkali may be added toconverter 30. During start-up, liquid catalyst may be introduceddirectly into vessel 10 as a catalyst stream. Alternatively, oradditionally, catalyst may be added elsewhere in system 1. For example,fresh catalyst solution may be injected into line 21 (not shown) or intoconverter 30. In embodiments, line 21 comprises liquid catalyst, atleast a portion of which may be a recycle stream from, for example,vessel 10 which may be connected via line 21 to converter 30.

The overall process reaction is:

H₂S(g)+1/2O₂(g)⇄H₂O+S°  (1)

Sour gas stream in line 25 may be any hydrogen sulfide or sulfurcontaining gas stream, for example, sour gas stream in line 25 maycomprise air, natural gas, carbon dioxide, amine acid gas, landfill gas,synthesis gas, geothermal gas, biogas, refinery gas, or any combinationthereof. Sour gas stream in line 23 may be pretreated as is known tothose of skill in the art. For example, in FIG. 1, sour gas stream inline 23 is passed through knock out pot 24. Hydrogen sulfide-containinggas stream in line 25 from knock out pot 24 is sent to converter 30. Inconverter 30, H₂S is converted to elemental sulfur. Treated (i.e.sweetened) gas stream in line 35 is sent for furtherprocessing/utilization (not shown). In embodiments, high shear gassweetening system 1 is effective for greater than 99% removal ofhydrogen sulfide from the sour gas. In embodiments, high shear gassweetening system 1 is effective for greater than 99.9% removal ofhydrogen sulfide from the sour gas.

Within converter 30, liquid catalyst converts H₂S to elemental sulfurvia several chemical reactions. The converter design is determined bythe sour gas flow and pressure, as well the H₂S removal efficiencyrequired. For an iron catalyst, the absorption in converter 30 may bedescribed by the following reactions.

The absorption of H₂S may be described as:

H₂S(g)+H₂O(1)⇄H₂S(1)+H₂O.  (2)

The ionization of H₂S is described by the reaction:

H₂S(1)⇄H⁺+HS⁻.  (3)

The oxidation by ferric ions (Fe³⁺) may be depicted as:

HS⁻+2Fe³⁺→S°(s)+2Fe²⁺+H⁺.  (4)

Therefore, the overall absorption reaction is:

H₂S(g)+2Fe³⁺→2H⁺+S°+2Fe²⁺.  (5)

A liquid stream comprising sulfur and reduced liquid catalytic solutionexits converter 30 via converter outlet line 13. Dispersible oxidant gasis injected into high shear gas sweetening system 1 via line 22, whichmay introduce oxidant gas into line 13 or directly into HSD 40. Theoxidant gas may be air or enriched air. In embodiments, the oxidant gasis fed directly into HSD 40, rather than being combined with the liquidreactant stream (i.e., sulfur-containing liquid catalytic stream exitingconverter 30 via line 13). Pump 5 may be operated to pump theregenerated liquid catalyst from line 21 and vessel 10 through line 12into converter 30, and to build pressure, providing a controlled flowthroughout high shear device (HSD) 40 and high shear gas sweeteningsystem 1. In some embodiments, pump 5 increases the pressure of the HSDinlet stream to greater than 202.65 kPa (2 atm), preferably greater thanabout 303.975 kPa (3 atmospheres). In this way, high shear gassweetening system 1 may combine high shear with pressure to enhancereactant intimate mixing.

In embodiments, liquid catalytic solution and, if present, alkali arefirst mixed in vessel 10. Reactants enter vessel 10 via, for example,inlet lines 14, 15, and 52. Any number of vessel inlet streams isenvisioned, with three shown in FIG. 1 (via lines 14, 15, and 52).

Oxidant and catalytic liquid are intimately mixed within HSD 40, whichserves to create a fine dispersion of the oxidant gas in the catalyticliquid. In HSD 40, the oxidant gas and catalytic liquid are highlydispersed such that nanobubbles, submicron-sized bubbles, and/ormicrobubbles of the gas are formed for superior dissolution intosolution and enhancement of reactant mixing. For example, disperser IKA®model DR 2000/4, a high shear, three stage dispersing device configuredwith three rotors in combination with stators, aligned in series, may beused to create the dispersion of dispersible oxidant gas in liquidcatalytic medium comprising sulfur (i.e., “the reactants”). Therotor/stator sets may be configured as illustrated in FIG. 2, forexample. The combined reactants enter the high shear device via line 13and enter a first stage rotor/stator combination. The rotors and statorsof the first stage may have circumferentially spaced first stage rotorteeth and stator teeth, respectively. The coarse dispersion exiting thefirst stage enters the second rotor/stator stage. The rotor and statorof the second stage may also comprise circumferentially spaced rotorteeth and stator teeth, respectively. The reduced bubble-size dispersionemerging from the second stage enters the third stage rotor/statorcombination, which may comprise a rotor and a stator having rotor teethand stator teeth, respectively. The dispersion exits the high sheardevice via line 19. In some embodiments, the shear rate increasesstepwise longitudinally along the direction of the flow, 260. Forexample, in some embodiments, the shear rate in the first rotor/statorstage is greater than the shear rate in subsequent stage(s). In otherembodiments, the shear rate is substantially constant along thedirection of the flow, with the shear rate in each stage beingsubstantially the same.

If the high shear device 40 includes a PTFE seal, the seal may be cooledusing any suitable technique that is known in the art. For example, thereactant stream flowing in line 13 or regenerated liquid catalyst inline 21 may be used to cool the seal and in so doing be preheated asdesired prior to entering high shear device 40 or converter 30respectively.

In applications, the rotor(s) of HSD 40 is (are) set to rotate at aspeed commensurate with the diameter of the rotor and the desired tipspeed. As described above, the high shear device (e.g., colloid mill ortoothed rim disperser) has either a fixed clearance between the statorand rotor or has adjustable clearance. HSD 40 serves to intimately mixthe oxidant gas and the liquid catalytic solution comprising sulfurproduct. In some embodiments of the process, the transport resistance ofthe reactants is reduced by operation of the high shear device such thatthe velocity of the reaction is increased by greater than about 5%. Insome embodiments of the process, the transport resistance of thereactants is reduced by operation of the high shear device such that thevelocity of the reaction is increased by greater than a factor of about5. In some embodiments, the velocity of the reaction is increased by atleast a factor of 10. In some embodiments, the velocity is increased bya factor in the range of about 10 to about 100 fold.

In some embodiments, HSD 40 delivers at least 300 L/h at a tip speed ofat least 4500 ft/min, and which may exceed 7900 ft/min (40 m/s). Thepower consumption may be about 1.5 kW. Although measurement ofinstantaneous temperature and pressure at the tip of a rotating shearunit or revolving element in HSD 40 is difficult, it is estimated thatthe localized temperature seen by the intimately mixed reactants is inexcess of 500° C. and at pressures in excess of 500 kg/cm² undercavitation conditions. The high shear mixing results in dispersion ofthe oxidant gas in micron or submicron-sized bubbles. In someembodiments, the resultant dispersion has an average bubble size lessthan about 5 μm, alternatively, less than about 1.5 μm. In someembodiments, the resultant dispersion has an average bubble size of lessthan 1 μm. Accordingly, the dispersion exiting HSD 40 via line 18comprises micron and/or submicron-sized gas bubbles. In someembodiments, the mean bubble size is in the range of about 0.4 μm toabout 1.5 μm. In some embodiments, the mean bubble size is less thanabout 400 nm, and may be about 100 nm in some cases. In manyembodiments, the microbubble dispersion is able to remain dispersed atatmospheric pressure for at least 15 minutes.

Once dispersed, the resulting dispersion exits HSD 40 via line 18 whichis fluidly connected to vessel 10. Optionally, the dispersion may befurther processed prior to entering vessel 10, if desired. For example,high shear gas sweetening system 1 may further comprise venture sparger45 positioned between HSD 40 and vessel 10. An outlet line 19 mayconnect venture sparger 45 with vessel 10. In cases where venturesparger 45 will limit throughput, a sparger may not be utilized.Oxidizer inlet line 19 fluidly connects to oxidizer 10 wherein furthercatalytic solution oxidation (regeneration) may occur. In instanceswhere HSD 40 is being incorporated into an existing gas sweeteningsystem comprising a venture sparger, the venture sparger 45 may beretained or eliminated depending on throughput limitations of theventure sparger.

Reduced liquid catalyst exiting converter 30 is regenerated byoxidation. Oxidation of the catalyst will occur within HSD 40 and maycontinue during residence within vessel 10. As mentioned hereinabove,vessel 10 may be an oxidizer. For iron chelate catalyst, the oxidationreaction (which may occur within HSD 40, line 18, venture sparger 45,line 19, vessel 10, or a combination thereof) can be described in thefollowing chemical reactions:

The absorption of O₂ is depicted as:

1/2O₂(g)+H₂O(1)⇄1/2O₂(1)+H₂O.  (6)

The regeneration of ferrous ions (Fe²⁺) follows the reaction:

1/2O₂(1)+H₂O+2Fe²⁺→2OH⁻+2Fe³⁺.  (7)

Therefore, the overall regeneration reaction is:

1/2O₂(g)+H₂O+2Fe²⁺→2OH⁻+2Fe³⁺.  (8)

As a result of the intimate mixing of the reactants prior to enteringvessel 10, a significant portion of the chemical reaction may take placein HSD 40. Accordingly, in some embodiments, reactor/vessel 10 may beused primarily for separation of product sulfur from the liquidcatalytic solution. Alternatively, or additionally, vessel 10 may serveas a primary reaction vessel where most of the regeneration/oxidation ofredox catalyst occurs. For example, in embodiments, vessel 10 is anoxidizer. In embodiments in which HSD 40 is being incorporated into anexisting gas sweetening process comprising an oxidizer, vessel 10 may bethe oxidizer. For new installations, vessel 10 may serve primarily as astorage/separation vessel from which sulfur product is removed.

Vessel/reactor 10 may be operated in either continuous orsemi-continuous flow mode, or it may be operated in batch mode. Thecontents of vessel 10 may be maintained at a specified reactiontemperature using heating and/or cooling capabilities (e.g., coolingcoils) and temperature measurement instrumentation. Pressure in thevessel may be monitored using suitable pressure measurementinstrumentation, and the level of reactants in the vessel may becontrolled using level regulators (not shown), employing techniques thatare known to those of skill in the art.

Vent gas exits vessel 10 via vent line 17 and may be further treated,vented, and/or recycled to high shear gas sweetening system 1. Forexample, a portion of vent gas in line 17 may be recycled to line 13 orline 22. Vessel 10 may have a conical-shaped bottom to aid in thesettling and removal of sulfur slurry therefrom. Product sulfur slurrycomprising sulfur crystals exits vessel 10 via line 16. Product sulfurslurry may be sent via settler pump 50 and lines 51 and 53 to sulfursettler 60. A portion of line 51 may be sent via line 52 back intovessel/oxidizer 10. Sulfur slurry in sulfur settler 60 settles into thebottom (e.g., cone-shaped section) of settler 60, and is pumped from thecone via sulfur line 65 and slurry pump 70 to sulfur separation unit 80.For example, sulfur separation unit 80 may employ a belt filter systemto produce a 60% sulfur cake. As another example, in some instances,sulfur separation unit 80 may comprise a bag filter system and may beused to produce a 30 wt % sulfur cake. If desired, the sulfur filtercake may be used to produce molten sulfur. Regenerated catalyticsolution 14 separated from sulfur cake may be sent back to oxidizer 10.

Oxygen used in conventional oxidation of the catalyst is supplied fromair or oxygen-enriched air 15 which is bubbled through the catalystsolution in oxidizer 10. High shear gas sweetening system 1 may comprisea secondary source of oxidant via blower 90 and oxidant inlet line 15.Oxidizer line 15 may be obtained via prefiltering at prefilter 85 andpumping via blower 90 and line 86 from prefilter 85 to oxidizer/vessel10. A small caustic addition to high shear gas sweetening system 1 (notshown) may be used to maintain the catalyst solution in the mildlyalkaline pH range.

This liquid phase oxidation processes uses oxygen carriers dissolved orsuspended in a liquid phase, which can then be regenerated continuouslyat ambient temperatures in certain embodiments. In contrast to othersystems mentioned hereinabove, this modified system comprises anenclosed external high shear device 40 to create microbubbles (and/orsubmicron-sized bubbles) of air/enriched air or oxygen in line 18 (andoptionally venture-sparged line 19) that then enters oxidation unit 10.External high shear device 40 may be positioned ahead of the venturesparger 45 of existing systems, and allows for rapid oxidation and highconversions of catalyst.

Potential benefits of this modified system include, but are not limitedto, faster cycle times, increased throughput, reduced operating costsand/or reduced capital expense due to the possibility of designingsmaller vessel(s) and/or operating the vessel(s) at lower temperatureand/or pressure.

In embodiments, the process of the present disclosure provides moreeffective elimination of sulfur compared to desulfurization in theabsence of external high shear mixing.

In some embodiments, the operating conditions of system 1 comprise atemperature in the range of from about 100° C. to about 230° C. Inembodiments, the temperature is in the range of from about 160° C. to180° C. In specific embodiments, the reaction temperature in vessel 10,in particular, is in the range of from about 155° C. to about 160° C. Insome embodiments, the reaction pressure in vessel 10 is in the range offrom about 202.65 kPa (2 atm) to about 5.6 MPa-6.1 MPa (55-60 atm). Insome embodiments, reaction pressure is in the range of from about 810.6kPa to about 1.5 MPa (8 atm to about 15 atm). In embodiments, vessel 10is operated at or near atmospheric pressure.

Multiple High Shear Mixing Devices. In some embodiments, two or morehigh shear devices like HSD 40, or configured differently, are alignedin series, and are used to further enhance the reaction. Their operationmay be in either batch or continuous mode. In some instances in which asingle pass or “once through” process is desired, the use of multiplehigh shear devices in series may also be advantageous. For example, inembodiments, outlet dispersion in line 18 may be fed into a second highshear device. When multiple high shear devices 40 are operated inseries, additional oxidant gas may be injected into the inlet feedstreamof each high shear device. In some embodiments, multiple high sheardevices 40 are operated in parallel, and the outlet dispersionstherefrom are introduced into one or more vessel 10.

Features. The application of enhanced mixing of the reactants by HSD 40potentially permits efficient regeneration of liquid catalyst. In someembodiments, the enhanced mixing potentiates an increase in throughputof the process stream. In some embodiments, the high shear mixing deviceis incorporated into an established process, thereby enabling anincrease in production (i.e., greater throughput). In contrast to somemethods that attempt to increase the regeneration by larger volumeoxidizers, the superior dispersion and contact provided by external highshear mixing may allow in many cases a decrease in the size and/orresidence time in vessel 10 while maintaining or even increasingdesulfurization rate. Without wishing to be limited to a particulartheory, it is believed that the level or degree of high shear mixing issufficient to increase rates of mass transfer and may also producelocalized non-ideal conditions that enable reactions to occur that wouldnot otherwise be expected to occur based on Gibbs free energypredictions. Localized non ideal conditions are believed to occur withinthe high shear device resulting in increased temperatures and pressureswith the most significant increase believed to be in localizedpressures. The increase in pressures and temperatures within the highshear device are instantaneous and localized and quickly revert back tobulk or average system conditions once exiting the high shear device. Insome cases, the high shear mixing device induces cavitation ofsufficient intensity to dissociate one or more of the reactants intofree radicals, which may intensify a chemical reaction or allow areaction to take place at less stringent conditions than might otherwisebe required. Cavitation may also increase rates of transport processesby producing local turbulence and liquid micro-circulation (acousticstreaming). An overview of the application of cavitation phenomenon inchemical/physical processing applications is provided by Gogate et al.,“Cavitation: A technology on the horizon,” Current Science 91 (No. 1):35-46 (2006). The high shear mixing device of certain embodiments of thepresent system and methods induces cavitation whereby oxidant andreduced liquid catalyst are dissociated into free radicals, which thenreact to regenerate the catalyst.

In some embodiments, the system and methods described herein permitdesign of a smaller and/or less capital intensive process thanpreviously possible without the use of external high shear device 40.Potential advantages of certain embodiments of the disclosed methods arereduced operating costs and increased production from an existingprocess. Certain embodiments of the disclosed processes additionallyoffer the advantage of reduced capital costs for the design of newprocesses. In embodiments, dispersing oxidant gas in liquid comprisingreduced liquid catalyst with high shear device 40 decreases the amountof unoxidized liquid catalyst. Potential benefits of some embodiments ofthis system and method for gas sweetening include, but are not limitedto, faster cycle times, increased throughput, reduced operating costsand/or reduced capital expense due to the possibility of designingsmaller oxidizers 10 or replacing an oxidizer with a separation vessel10 and/or operating the process at lower temperature and/or pressure.

In embodiments, use of the disclosed process comprising reactant mixingvia external high shear device 40 allows use of less oxidant invessel/reactor 10 than previously permitted. In embodiments, the methodcomprises incorporating external high shear device 40 into anestablished process thereby reducing the operating temperature and/orpressure of the reaction in external high shear device 40 and/orenabling the increase in production (greater throughput) from a processoperated without high shear device 40. In embodiments, vessel 10 is usedmainly for separation of sulfur slurry from liquid catalyst, as much ofthe oxidation of catalyst occurs in external high shear device 40. Inembodiments, most of the regeneration oxidation reaction occurs withinthe external high shear device 40.

The present methods and systems for gas sweetening via oxidation withliquid phase catalyst and regeneration of reduced catalyst by oxidationemploy an external high shear mechanical device to provide rapid contactand mixing of chemical ingredients in a controlled environment in thehigh shear device. The high shear device reduces the mass transferlimitations on the reaction and thus increases the overall reactionrate, and may allow substantial oxidation of catalyst under globaloperating conditions under which substantial reaction may not beexpected to occur.

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use ofthe term “optionally” with respect to any element of a claim is intendedto mean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,and the like.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference, to the extent theyprovide exemplary, procedural or other details supplementary to thoseset forth herein.

1. A system for removing hydrogen sulfide from a sour gas stream, thesystem comprising: a converter comprising an inlet for sour gas, aninlet for a liquid stream comprising oxidized catalyst, and a converteroutlet line for a converter liquid product comprising sulfur and reducedcatalyst; a dispersible gas inlet whereby oxidant may be introduced intothe converter outlet line; an external high shear device downstream ofthe dispersible gas inlet, wherein the external high shear devicecomprises an inlet in fluid communication with the converter outlet lineand a high shear device outlet and wherein the external high sheardevice is configured for intimately contacting the oxidant with theconverter liquid product such that the reduced catalyst therein isoxidized; an oxidizer in fluid communication with the high shear deviceoutlet; and a recycle line fluidly connecting the oxidizer and the inletfor a liquid stream of the converter, whereby regenerated oxidizedcatalyst may be recycled from the oxidizer to the converter.
 2. Thesystem of claim 1 wherein the external high shear device comprises atleast one rotor and one complementarily-shaped stator separated by ashear gap width defined as the minimum clearance between the at leastone rotor and the at least one stator and wherein the at least one rotoris rotatable at a tip speed whereby a shear rate, defined as the tipspeed divided by the shear gap width, of at least 20,000 s⁻¹ isproduced.
 3. The system of claim 2 wherein the external high sheardevice has a tip speed of greater than about 20.3 m/s (4000 ft/min). 4.The system of claim 3 wherein the external high shear device has a tipspeed of greater than about 22.9 m/s (4500 ft/min).
 5. The system ofclaim 4 wherein the external high shear device has a tip speed ofgreater than 40 m/s (7900 ft/min).
 6. The system of claim 2 wherein theexternal high shear device produces a local pressure of at least about1034.2 MPa (150 kPsi) at the tip of the at least one rotor duringoperation.
 7. The system of claim 2 wherein the energy expenditure ofthe external high shear device is greater than 1000 W/m³ duringoperation.
 8. The system of claim 1 wherein the external high sheardevice comprises a toothed rim disperser comprising at least onegenerator comprising a rotor and a stator having a shear gap widthdefined as the minimum clearance between the rotor and the stator,wherein the rotor is rotatable at a tip speed whereby a shear rate,defined as the tip speed divided by the shear gap width, of at least100,000 s⁻¹ is produced.
 9. The system of claim 1 wherein the externalhigh shear device is capable of producing a dispersion of oxidantbubbles in converter liquid product, the oxidant bubbles having anaverage bubble diameter on the submicrometer scale.
 10. The system ofclaim 9 wherein the oxidant bubbles have an average bubble diameter ofless than 400 nm.
 11. The system of claim 10 wherein the oxidant bubbleshave an average bubble diameter of no more than 100 nm.
 12. The systemof claim 1 comprising at least two high shear devices.
 13. The system ofclaim 1 wherein the oxidizer is configured for settling and removal of aslurry comprising elemental sulfur and aqueous solution from a bottomsection thereof.
 14. The system of claim 13 further comprising aseparator fluidly connected with and downstream of the oxidizer andconfigured to separate a separated portion of the aqueous solution fromthe sulfur-containing slurry removed from the oxidizer.
 15. The systemof claim 1 wherein the oxidizer further comprises spargers wherebyadditional oxidant gas is introduced into the oxidizer.
 16. The systemof claim 1 wherein the catalyst is selected from organometallics andiron chelate catalysts.
 17. In a system for removing hydrogen sulfidefrom a sour gas stream, the system comprising an absorption unit, aredox catalyst that becomes reduced upon converting hydrogen sulfide toelemental sulfur, an oxidization unit for regenerating the reducedcatalyst, and a catalyst recycling system for returning regeneratedcatalyst to the absorption unit, the improvement comprising: insertingan external high shear device in line between the converter and theoxidization unit, wherein the external high shear device is operable toproduce a shear rate of at least 10,000 s⁻¹.
 18. The system of claim 17wherein the external high shear device comprises at least twogenerators, wherein at least one of the generators produces a shear rateof at least 10,000 s⁻¹.
 19. The system of claim 18 wherein the shearrate provided by one generator is greater than the shear rate providedby another generator.
 20. The system of claim 17 wherein the externalhigh shear device comprises at least one generator comprising a rotorand a complementarily-shaped stator.